Australian scientists may have solved the mystery of bee colony collapse

It's the bee version of a mystery thriller. Hives full of healthy honey bees suddenly empty. Inside, beekeepers the world over would find abandoned young and a queen but no worker bee corpses.

At first apiarists worried a new disease was infecting their colonies. Evidence would later show bees were stressed out - by pesticides, pests and poor food quality - but not even that could explain the rapid collapse of colonies.

Scientists observe bee societies: An Australian native bee visits a flower. They have not been affected by colony collapse disorder. Photo: David Porter

"Your colony goes from having lots of bees to no bees in a few weeks. There's no obvious pathogen and there's no corpses left in the hive," said Dr Barron, from Macquarie University.

Known as colony collapse disorder, it has affected about 30 per cent of honey bee colonies in Europe and North America each year over the past decade. Australian honey bee colonies, which play a significant role in crop production, worth about $5 billion a year, have so far been unaffected.

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"When you get a colony failing like that, you're not just seeing the death of individuals but the absolute collapse of a whole society," he said.

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Rather than focus on the stress chemical exposure, pests and pathogens had on individual bees, Dr Barron and his team wondered what impact chronic stress was having on bees highly sophisticated hierarchical communities.

Andrew Barron: 'lots of bees to no bees in a few weeks'. Photo: Wolter Peeters Photo: Wolter Peeters

It is well known that honey bees delay leaving their hive to forage until later in adulthood. Foraging for nectar and pollen is hard work, and bees frequently die from exhaustion or getting lost.

But if external stressors such as pests or pesticides kill too many forager bees at once, it triggers a rapid maturation of the next generation and prompts them to leave the nest before they're are ready.

"Bees who start to forage when they've been adults for less than two weeks are just not good at it. They take longer, and they complete fewer trips." When Dr Barron and his team placed tiny radio trackers on young forager bees they discovered they also died earlier.

When the team entered this information into a model they found these premature deaths triggered a vicious cycle, whereby subsequent generations of inefficient foragers could not return enough resources to keep the colony going, leading to its collapse.

"Our model suggests bees are very good at buffering against stress, but there's a tipping point and then you see this rapid transition into complete societal failure," Dr Barron said.

Dr Barron said their findings, which have been published in the Proceedings of the National Academy of Sciences journal, are the first to propose an explanation for the unusually rapid collapse of bee colonies.